The present invention relates to an electromotive drive having a magnet body held on its rotor shaft. Such drives are suitable, in particular, as an auxiliary drive in a motor vehicle in which the magnet body is a magnet wheel attached to the rotor shaft and producing a speed-proportional signal in a stator-side Hall probe device. Such drives may be employed, for instance, in speed-controlled window drives or window drives controlled by the direction of rotation.
European Patent Application No. EP-A1-0 489 940 describes a commutator motor in which Hall probes are arranged on a stator-side electronics connection plate for the speed-control. A magnet wheel is attached directly to the rotor shaft and is associated with the Hall probes. The magnet wheel can be attached on the rotor shaft, by a corresponding force fit and/or adhesive fit.
Japanese Patent Application No. JP4-A-1 83 245 describes an arrangement for mounting a magnet body on a rotor shaft. A separate holding part has axial protrusions which engage corresponding recesses in one end side of the magnet body which faces the holding part. The other end side of the magnet body rests against an engine-side stop in the form of the laminated rotor core.
U.S. Pat. No. 2,161,953 describes a mounting arrangement of a magnet body on a rotor shaft. A separate holding part has an axial driving arm which engages as corresponding recess in one end side of the magnet body. The other end side of the magnet body rests against an engine side stop in the form a ring fixed in position on the rotor shaft.
German Patent Application No. DE-U1-90 06 935 describes an electromotive drive for a motor vehicle. The electromotive drive has a commutator and a magnet wheel arranged on the rotor shaft to detect the speed and/or direction of rotation. This arrangement cooperates with a stator-side Hall sensor. A spacer bushing is placed, fixed for rotation, on the rotor shaft for holding the magnet wheel on the rotor shaft. The magnet wheel is then either forced, placed, or cemented concentrical to the spacer bushing onto the outer circumference of the latter or is attached by means of force locking. For the force-locked attachment, the spacer bushing is provided with a flattening on its outer circumference and the magnet wheel is provided with a matching flattening on its corresponding inner side. To axially fix the spacer brushing in position, the spacer bushing rests with its one end side against the commutator and it is fixed in position at its other end side with a retaining ring. The retaining ring can be inserted into the rotor shaft in form-locked manner. The magnetic wheel can consist of a plastic body with magnet particles incorporated in the plastic or of a non-magnetic basic body into which permanent magnets are inserted.
Unfortunately, the magnet body is relatively brittle. Therefore tangentially and axially fixing the magnet body into position on the rotor shaft with a force fit such that the magnet body will reliably remain on the rotor shaft even after long and rough operation tends to crack the brittle magnet body. Fixing the magnet body into position on the rotor shaft with adhesive is not sufficiently reliable. Hence, the arrangement described in European Patent Application No. EP-A1-0 489 940 is not acceptable.
Further, the arrangement described in Japanese Patent Application No. JP-A-1 83 245 and U.S. Pat. No. 2,161,953 have a large installation size and/or are not particularly simple. In addition, these arrangements do not permit the axial position of the magnet body to be adjusted.
Thus, there exists a need to provide a relatively simple arrangement to tangentially and axially fix a brittle magnet body on a shaft
such that the magnet body will remain on the shaft even after long and rough operation, PA0 without exerting forces on the magnet body which could lead to cracking, PA0 such that the axial position of the magnet body can be adjusted, and PA0 with a small installation size.